Download parameters which affect real and reactive power flow

FACULTY OF ENGINEERING
LAB SHEET
EEL2026
POWER TRANSMISSION AND DISTRIBUTION
TRIMESTER 2
PTD1- Performance of Transmission Line under Different Loading Conditions
PTD2- Parameters which affect Real and Reactive Power Flow
*Note: On-the-spot evaluation may be carried out during or at the end of the experiment.
Students are advised to read through this lab sheet before doing experiment. Your
performance, teamwork effort, and learning attitude will count towards the marks.
EEL 2026 Transmission and Distribution
Instruction
1. Before coming to the laboratory read the lab sheet carefully and understands the
procedure of performing the experiments.
2. Do not switch-on the power supply unless permitted by the lab supervisor.
3. Do not make or break any connection with the power supply on.
4. Handle the equipments with care.
5. Do the necessary calculation, draw the graphs and submit the report within the specified time of the
lab session.
Experiment # 1
Performance of Transmission Line under Different
Loading Conditions
Objectives



To compare the voltage regulations of the given transmission line under resistive,
inductive and capacitive loading conditions.
To diagnose the reason for the voltage drop across the transmission line when the
sending-end and receiving-end voltages have the same magnitude.
To investigate the effectiveness of the shunt capacitors to improve the power transfer
capability of the line.
Introduction
A short transmission line is modeled by a single reactance as shown in Fig. 1. A good
understanding of the behavior of most of the transmission lines can be obtained by the short
line model. It is this model which will be used in this experiment.
Depending upon the loading condition the phase angle difference between the sending-end
and receiving-end voltages and the voltage drop along the line will vary. These effects can
be easily understood from the phasor diagram shown in Fig. 1. It may also be observed that
a significant voltage drop will exist across the line even when the sending -end voltage, E1
and the receiving-end voltage, E2 are equal in magnitude.
I
E1
XL
E1
IX L
E2
E2
I
(a)
(b)
Fig. 1 (a) Transmission line (b) Phasor diagram
2
We have studied that the voltage drop along the transmission line and the receiving-end
voltage vary widely for inductive loads. In order to regulate the voltage at the receiving-end
of the line in some way so as to keep it at as constant as possible we should adopt some type
of compensation. One method commonly used is to connect shunt capacitors at the end of the
line. These capacitors produce a significant voltage rise thus compensating for the voltage
drop. Static capacitors are switched in and out in a practical system and their value is adjusted
depending on the loads. For purely inductive loads, the capacitor should deliver reactive
power equal to that consumed by the inductive load. For resistive loads, the reactive power,
which the capacitor must supply to regulate the voltage, is not easy to calculate. In this
experiment, we shall determine the reactive power (the value of capacitor) by trial and error,
adjusting the capacitors until the receiving-end voltage is approximately equal to the sendingend voltage. For loads, which draw both real and reactive power, the same trial and error
method is adopted.
Note that for a short transmission line having a line reactance of X /phase and resistance
neglected. The following formulas will be useful.
Sending-end voltage (L-L) = E11; Receiving end voltage (L-L) = E22
Three-phase sending-end power = Three-phase receiving end Power
E E Sin (1   2 )
= P1 = P2 = 1 2
X
2
E
E E Cos(1   2 )
Three-phase sending-end reactive power = Q1 = 1 - 1 2
X
X
2
E1 E2 Cos(1   2 ) E 2
Three-phase receiving-end reactive power = Q2 =
X
X
Apparent power at sending end = S1 
Apparent power at receiving end = S 2
P  Q ;
 P  Q ;
2
1
2
1
2
2
2
2
Equipment required
Three-phase transmission line (8329)
Resistive load (8311)
Inductive load (8321)
Capacitive load (8331)
AC voltmeter (8426)
Phase meter (8451)
Three-phase wattmeter/varmeter (8446)
Power supply (8821)
Connection leads (9128)
Procedure
1. Set the impedance of the transmission line to 200  and connect the meters as shown in
Fig. 2. The circuit should be connected to the three-phase variable supply. Note that
watt/var meters and phase meter need 24V AC supply provided in the power supply unit.
Connect all the loads in star. Verify your connections with the lab supervisor before
switching on the power supply.
3
0-500V
E2
0-500V
E1
4
1
5
2
3
6
P1
1
5
2
3
6
8821
0-415V
Q1
4
8446
4
P2
8329
Q2
5
6
8446
3-phase
Yconnected
LOAD
8311
8321
8331
Fig. 2 Connection diagram for steps 2, 3 and 4
2. Adjust the sending-end voltage E1 to 300 V and keep it constant for the reminder part of
the experiment. Use a three-phase resistive load and increase the load in steps making
sure that the loads are balanced. Take readings of sending end and receiving end voltages
and powers, E1, Q1, P1, E2, Q2, and P2. Record your results in Table 1.
3. Switch off the power supply and connect a three-phase balanced inductive load in parallel
with the balanced resistive load. Don’t remove any other connections shown in Fig.2.
Increase the load in steps making sure that the loads are balanced. Take readings of
sending end and receiving end voltages and powers, E1, Q1, P1, E2, Q2, and P2. Record
your results in Table 2.
4. Switch off the power supply, remove the inductive load and connect a three-phase
balanced capacitive load in parallel with the balanced resistive load. Take readings of
sending end and receiving end voltages and powers,E1, Q1, P1, E2, Q2, and P2 for different
loadings. Record your results in Table 3.
5. Draw three graphs of receiving end voltage, E2 (obtained from steps 2, 3, and 4) on the
same graph paper as a function of the receiving-end power P2 and discuss your results.
6. Switch off the power supply and connect a phase meter to measure the phase angle
difference between E1 and E2 and a voltmeter to measure the voltage across the
transmission line as shown in Fig. 3. Note that the load consists of resistances in parallel
with capacitances. Now for each resistive load, adjust the capacitive load so that the load
voltage E2 is as close as possible to 300 V. Take readings of XC, E1, P1, Q1, E2, P2, Q2, and
the phase angle for different loadings. Record your results in Table 4.
7. Draw the graphs of E2 and the phase angle difference between E1 and E2 as a function of
P2 from the results in Table 4. Note that the addition of static capacitors has yielded a
much more constant voltage, and further more, the power P2 which can be delivered has
increased. On this curve, indicate the phase angle between E2 and E1 as well as the
reactive power Q2 used for individual resistive load settings.
8. In this part of the experiment, we shall observe a significant voltage drop along the
transmission line even when the voltages E1 and E2 are equal in magnitude. This voltage
4
drop is due to the phase angle difference between the two voltages. Switch off the supply
and insert an ammeter in series with the transmission line as shown in Fig. 3 to measure
the line current without removing any other connection. Using the circuit shown in Fig. 3,
set the load resistance per phase at 686  and E1 = 300 V, adjust the capacitive reactance
until the load voltage is as close as possible to 300 V. Measure and record E1, Q1, P1, E2,
Q2, P2, E3, the line current I and the phase angle.
8451
0-500V
1
2
3
4
E2
0-500V
E1
686
8329
4
1
5
6
2
3
4
1
5
6
2
3
4
686
P1
Q1
P2
Q2
5
6
A
8821
686
8446
0-415V
8446
E3
3-phase
8311
8331
0-250V
Fig.3 Connection diagram for Steps 6 – 8
9. Using the results of step 8, draw the phasor diagram of per phase values of E 1 and E2 to
scale and draw E3. From the diagram compute E3 and compare it with the measured
value. Also compute the real power, reactive power and apparent power consumed by the
line. From the apparent power compute the line current and compare it with the measured
value.
Observations
Table 1: Results of procedure step 2
R


4800
2400
1600
1200
960
800
686
E1
V
P1
W
Q1
var
E2
V
5
P2
W
Q2
Var
Table 2 Results of procedure step 3
R


4800
2400
1600
1200
960
800
686
Xl


4800
2400
1600
1200
960
800
686
E1
V
P1
W
Q1
var
E2
V
P2
W
Q2
var
P2
W
Q2
var
Table 3 Results of procedure step 4
R


4800
2400
1600
1200
960
800
686
Xc


4800
2400
1600
1200
960
800
686
E1
V
P1
W
Q1
var
E2
V
Table 4 Results of procedure step 6
R


4800
2400
1600
1200
960
800
686
Xc

E1
V
P1
W
Q1
var
E2
V
6
P2
W
Q2
var
Angle
degree
Results of procedure step 8
E1=
E2=
P1=
P2 =
Q1=
Q2=
E3=
Phase angle =
Sample calculation
Line current, I =
This sample calculation is to help you to answer Exercise 3.
Let
E1 = 350 V
E2 = 350 V
E3 = 165 V
P1 = 600 W
P2 = 510 W
Q1 = 170 var
Q2 = -280 var
Phase angle = 48o and Line current, I = 0.95
E1 per phase = 350/3 = 202 V
E2 per phase = 350/3 = 202 V
E3 = 165 V
P1 per phase = 600/3 = 200 W
P2 per phase = 510/3 = 170 W
Q1 per phase = 170/3 = 56.7 var
Q2 per phase = -280/3 = 93.3 var
The phasor diagram of voltages to scale is shown in Fig.4.
E1
-48o
E3=165
E2
Fig. 4 Phasor diagram
From the figure E3 = 165 V which is the same as the measured value. [The voltage E3 may
also be calculated using the formula, E3 = 2*E1*sin(24o)]
Real power consumed = 200 –170 = 30 W
Reactive power consumed = 56.7 –(-93.3) = 150 var
Apparent power in the line = 1502  302  153 VA
Current through the line = 153/165 = 0.93 A
The difference between the calculated value and the measured value is 0.02 A.
7
Exercise
1. Analyze your results based on the graphs you have drawn in steps 5 and 7. From the
graphs plotted predict the voltage regulations for load powers of 60W, 70W and 80W
respectively under different loading conditions (resistive, resistive-inductive and
resistive-capacitive) and compile the results.
2. Analyze your results obtained in step 9.
3. A three-phase transmission line has reactance of 100  per phase. The sending-end
voltage is 100 kV and the receiving-end voltage is also regulated to be 100 kV by placing
a bank of static capacitors in parallel with the receiving-end load of 50 MW. Predict
(a) the reactive power supplied by the capacitor bank
(b) the reactive power supplied by the sending-end side
(c) the voltage drop in the line per phase
(d) the phase angle between the sending-end and receiving-end voltages and
(e) the apparent power supplied by the sending-end side.
4. If the 50 MW load in Exercise 3 is suddenly disconnected formulate the receiving-end
voltage which would appear across the capacitor bank. What precaution, if any, must be
taken?
5. Argue why it is not possible to raise the receiving-end voltage by static capacitors if the
transmission line is purely resistive.
6. State briefly what you have learned from this experiment.
8
EET2026 POWER TRANSMISSON AND DISTRIBUTION
Experiment # 2
PARAMETERS WHICH AFFECT REAL AND REACTIVE
POWER FLOW
Objectives
To investigate the flow of real and reactive power when sender and receiver voltages are
different, but in phase.
To forecast the flow of real and reactive power when sender and receiver voltages are equal,
but out of phase.
To analyze the flow of real and reactive power when sender and receiver voltages are
different and out of phase.
Introduction
Transmission lines are designed and built to deliver electric power. Power flows from the generator
(sender end) to the load (receiver end). But, in complex interconnected systems, the sender and
receiver ends may become reversed depending upon the system load conditions which, of course,
vary throughout the day. Power in such a line may flow in either direction. The character of the load
also changes from hour to hour, both as to kVA loading and as to power factor. How, then, can we
attempt to understand and solve the flow of electric power under such variable loading conditions,
further complicated by the possible reversal of source and load at the two ends of the line?
We can obtain meaningful answers by turning to the voltage at each end of the tine. In Fig.1 a
transmission line having a reactance of X  (per phase) has sender and receiver voltages of E1 and E2
V respectively. (A transmission line is both resistive and reactive, but we shall assume that the reactance is so much larger that the resistance may be neglected) If we allow these voltages to have any
magnitude or phase relationship, we can represent any loading condition we please. In other words,
by letting E1 and E2 take any values and any relative phase angle, we can cover all possible loading
conditions which may occur
Sender and receiver voltages are different and out of phase.
Referring to Fig. 1, both E1 and E2 are phasors with different magnitude and out of phase.
9
X
E1
E2
I
SENDER
RECEIVER
Fig.1: Transmission line
The voltage drop along the line is E1- E2; consequently, for a line having a reactance of X Ω, the
current I is given by
I=
E1  E 2
jX
when E1 – E2 is the phasor difference between the sending- and receiving-end voltages.
If we know the value of E1 and E2, and the phase angle between them, it is a simple matter to
find the current I, knowing the reactance X of the line. From this knowledge we can calculate the
real and reactive power, which is delivered by the source and received by the load.
Suppose, for example, that the properties of a transmission line are as follows:
Line reactance per phase, X = 100
Sender voltage (E1) = 20 kV
Receiver voltage (E2) = 30 kV
Receiver voltage lags behind sender voltage by 26.5°.
These line conditions are represented schematically in Fig. 2. From the phasor diagram in Fig. 3,
we find that the voltage drop (E 1 – E2) in the line has a value of 15 kV. The current I has a value of
15 kV/100 = 150 A and it lags behind (E 1 – E2) by 90°. From the geometry of the figure, we find
that the current leads E1 by 27°. The active and reactive power of the sender and the receiver can
now be found.
X=100 
E1=20kV
S
E1=20kV
26.5
E2=30kV
E2=30kV
R
Fig. 2: Transmission line and phasor diagram of voltages
10
I = 150 A
90°
27°
E1 = 20 kV
53.5°
E1 – E2 = 15 kV
26.5°
E2 = 30 kV
Fig. 3: Phasor diagram
Note: When determining the sine and cosine of the angle between voltage and current, the current is
always chosen as the reference phasor. Consequently, because E1 lags behind I by 27°, the angle is
negative.
The real power delivered by the sender is, 150 A x 20 kV x cos (-27°) = +2670 kW.
The real power received by the receiver is, 150 A x 30 kV x cos (-53.5) = +2670kW.
The reactive power delivered by the sender is, 150 A x 20 kV x sin (-27°) = -1360 kvar.
The reactive power received by the receiver is, 150 A x 30 kV x sin (-53,5°)= -3610 kvar.
(Note that equations for real power and reactive power given in the lab sheet for Experiment-1
can also be used for the above calculation.)
Based on the results calculated above, if wattmeters and varmeters were placed at the sender
and receiver ends they would give readings as shown in Fig. 4. This means that active power is
flowing from the sender to the receiver, and owing to the absence of line resistance, none is lost
in transit.
150A
+2670
-1360
kW
kvar
+2670
kW
-3610
kvar
S
R
Real Power
Reactive Power
Real Power
Reactive Power
Fig. 4: Direction of real and reactive power flow
11
However, reactive power is flowing from receiver to sender and, during transit, 3160 - 1360 =
2250 kvar are consumed in the transmission line. This reactive power can be checked against
Line kvar = I2X = 1502 x 100 = 2250 kvar.
It will be noted that this is not the first time that we have found real power and reactive power
flowing simultaneously in opposite directions.
Sender and receiver voltages are different, but in phase.
When the voltages at the sender and receiver ends are in phase, but unequal, reactive power
will flow. The direction of flow is always from the higher voltage to the lower voltage.
Consider a transmission line in which the voltages at the sender and receiver ends are 30 kV and
20 kV respectively and the line reactance is 100  (Refer to Fig. 5).
X = 100
S
E1 3
E2=20kV
I
E1=30 kV
R
E2=20kV
Fig. 5: Transmission line and phasor diagram
The voltage drop in the line is 10 kV and the current is 10 kV/100Ω = 100 A as
shown in Fig. 6.
E2 = 20kV
E1 = 30kV
E1 – E2 = 10kV
I = 100A
Fig. 6 Phasor diagram showing current and voltages
The real power delivered by the sender end is, 100 A x 30 kV x cos (+ 90°) = 0 W.
The real power received by the receiver is, 100 A x 20 kV x cos (+90°) = 0 W.
The reactive power delivered by the sender end is,
100 A x 30 kV x sin ( + 90°) = + 3000kvar.
12
E1=30kV
The reactive power received by the receiver is
100A x 20 kV x sin ( + 90") = +2000kvar.
If wattmeters and varmeters were placed at each end, the readings would be as shown in Fig.
7.
100A
0 kW
S
+3000
kvar
Reactive Power
Real Power
0 kW
Real Power
+2000
R
kvar
Reactive Powe
Fig. 7 Direction of real and reactive power flow
S
Reactive power flows from the sender to the receiver, and 1000 kvar are absorbed in the
transmission line during transit. As can be seen, reactive power flows from the high-voltage to
the low-voltage side.
Sender and receiver voltages are the same, but out of phase.
Real power can only flow over a line if the sender and receiver voltages are out of phase. The
direction of power flow is from the leading to the lagging voltage end. Again, it should be noted
that this rule applies only to transmission lines, which are mainly reactive. The phase shift
between the sender and receiver voltages can be likened to an electrical "twist", similar to the
mechanical twist which occurs when a long steel shaft delivers mechanical power to a load.
Indeed, the greater the electrical "twist" the larger will be the real power flow. However, it is
found that it attains a maximum when the phase angle between the sender and receiver ends is
90°. If the phase angle is increased beyond this (by increased loading) it will be found that less
real power is delivered.
Consider a transmission line in which the voltages at each end are equal to 30 kV and the
receiver voltage lags behind the sender by 30°. The line reactance is 100 , and the circuit is
shown in Fig. 8.
E1 = 30kV
X = 100
S
E1 = 30kV
I
E2 =30kV
30
R
E2 =30kV
Fig. 8 Line with phase angle difference between E1 and E2 and phasor diagram
13
The voltage drop in the line (E 1 - E2) is found to be 15.5 kV. So the current I =15500/100 = 155 A
and it lags (E1 - E2) by 90o, as shown in Fig. 9.
E1 = 30kV
E1 – E2 = 15.5kV
o
15
15o
I
E2 = 30kV
Fig. 9 Phasor diagram showing voltages and current
Taking the current as the reference phasor, we can find the real and reactive power associated
with the sender and the receiver ends as shown in Fig.10.
155A
S
+4500
kW
Real Power
+4500
kW
+1200
kvar
Reactive Power
Real Power
-1200
R
kvar
Reactive Power
Fig. 10 Real and reactive power flow in the line
Sender End
Real power delivered = 30 kV x 155 A x cos (+15°) = +4500 kW,
Reactive power delivered = 30 kV x 155 A x sin (+ 15°) = +1200 kvar.
Receiver End
Real power received = 30 kV x 155 A x cos (-15°) = + 4500 kW.
Reactive power received = 30 kV x 155 A x sin (- 15) = - 1200 kvar.
The sender delivers both active and reactive power to the line and the receiver absorbs active
power from it. However, the receiver delivers reactive power to the line, so that the total
reactive power received by the line is 2400 kvar.
14
This example shows that a phase shift between sender and receiver voltages causes both real
and reactive power to flow. However, for angles smaller than 45 the real power considerably
exceeds the reactive power.
EQUIPMENT REQUIRED
DESCRIPTION
MODEL
Resistive Load
8311
Inductive Load
8321
Three-Phase Transmission Line
8329
Capacitive Load
Three-Phase Regulating Autotransformer
8331
8349
AC Voltmeter
8426
Three-Phase Wattmeter/Varmeter
6446
Phase Meter
8451
Power Supply
6821
Connection Leads
9128
PROCEDURE
WARNING.
High voltages are present in this Laboratory Experiment! Do not make any connections with the
power on!
In order to convey a sense of realism to the terms "sender" and "receiver" two consoles will be used in
the following experiments. A transmission line will connect the two consoles (Station A and B) and the
active and reactive power flow between them will be studied. The experiment will be conducted in
three parts.
Part-I: Sender and receiver voltages unequal, but in phase
Part-II; Sender and receiver voltages equal, but out of phase
Part-III: Sender and receiver voltages unequal, and out of phase
Note that there will be minor changes only in the connections between the parts of the
experiments. Don’t remove all the connections, simply do the changes only. Verify your
connections for each part with your lab supervisor
15
PART-I: Sender and Receiver voltages unequal, but in phase
1. Connect a three-phase transmission line between terminals 4, 5, 6 (variable AC output) of two
consoles, one of which is designated as Station A and the other, Station B. Connect the two threephase wattmelers/varmeters (6446) at each end as well as a phase meter (8451) as shown
schematically (single line diagram) in Fig. 11. Note that watt/var meters and phase meter need 24V
AC supply provided in the power supply unit. Verify your connections with the lab supervisor
before switching on the power supply.
0 – 500 V
8451
E1
STATION A
4 O
0-415 V
3-phase
Q1
STATION B
8446
8329
4
0-415 V
Q2
P2
3-phase
O
8446
5
8821
8821
6 O
E2
O
P1
5 O

0 – 500 V
Fig. 11 Sender and Receiver voltages unequal, but in phase
O
6
2. With the transmission line switch S open, adjust the line-to-line voltages so that E1 and E2 are both
equal to 300 V and observe that the phase angle difference between terminals 4-5 of station A and
terminals 4-5 of station B is zero. Is phase angle zero?
 Yes
 No
3. Without making any changes, measure the phase angle between terminals 4-5 of station A and
terminals 5-4 of station B.
Phase angle is __________
4. Without making any change, measure the phase angle between terminals 4-5 of station A and
terminals 5-6 of station B.
 Phase angle is lagging
 Phase angle is leading
5. Measure the phase angle between terminals 4-5 of station A and terminals 6-4 of station B.
 Phase angle is lagging  Phase angle is leading
16
6. By measuring all phase angles between line and neutral of station A and B prove that the phasor
diagrams for both stations are as given in Fig. 12. The purpose of this preliminary phase angle check is
to familiarize with the phase angles between the voltages at the two stations.
4A
4B
Rotation
Rotation
120°
N
120°
120°
120°
6A
N
120°
120°
5A
6B
5B
Fig. 12. The phase angles between the voltages at the two stations.
7. Close the Three-Phase Transmission Line switch, S with E1 = E2 = 300V, and the transmission line
impedance = 200 . Observe the three-phase wattmeler/varmeter readings. There should be no
significant power exchange.
P1 = _________ W
P2 = _________ W
Q1 = _________ var
Q2 = _________ var
8. Raise station A voltage to 350 V and observe power flow.
P1 = _________ W
P2 = _________ W
Q1 = _________ var
Q2 = _________ var
Which of the two stations would be considered to be the sender?
_________________________________________________________________
17
9. Reduce station A voltage to 300 V and raise station B voltage to 350 V. Observe power flow.
P1 = _________ W
P2 = _________ W
Q1 = _________ var
Q2 = _________ var
Which station would be considered to be the sender?
________________________________________________________________
10. Vary the voltages of both station A and station B and check the truth of the statement that reactive
power always flows from the higher voltage to the lower voltage.
PART-II: Sender and Receiver voltages equal, but out of phase
Study the Three-Phase Regulating Autotransformer to shift the phase of station A by 15°. The phase shift
(lag or lead) is obtained by changing the connections of a three-phase transformer by means of a tap
switch.
When the position of the tap-switch in the regulating transformer is altered, the secondary voltage
will a) be in phase with the primary, b) lag the primary by 15° or, c) lead the primary by 15".
11. Connect the above phase-shifting autotransformer to the variable AC terminals 4,5,6 of station A as
shown schematically in Fig. 13. Open the switch (S) in the transmission line or disconnect the
transmission line. Adjust the voltage at stations A and B to 350 V. With the Phase Meter determine
the phase angle of the secondary voltage 4, 5, 6 of the phase shifting transformer with respect to the
variable AC terminals 4, 5, 6 of the Power Supply of Station B. Record your readings for the three
positions of the phase-shift tap switch in Table 1.
0 – 500 V
8451
E1
4 O
Phase shifting
Autotransformer

0 – 500 V
E2
O
4
0-415 V
P1
3-phase
Q1
P2
5 O
8349
8329
8446
0-415 V
Q2
O
8446
5
8821
8821
6 O
O
Fig. 13 Phase shifting of voltages at Station A
18
6
3-phase
CAUTION!! KEEP THE SWITCH OF THE TRANSMISSION LINE OPEN FOR STEPS 11 AND 12
Table 1
Tap switch position
in degree
Phase angle
E1 in V
E2 in V
(Lag/Lead)
0
+ 15
-15
Note: The buck-boost tap switch must be kept at zero and the correct phase sequence must be applied to the
primary of the transformer.
12. Check that the phase-shift is the same for all the three phases, and that all voltages are
balanced.
13. Connect a three-phase, 400- transmission line between secondary terminals 4, 5, 6 of
the three-phase phase shifting autotransformer and the power supply terminals of station
B by closing the switch (see Fig.14). Change the tap switch position and record your results
in Table 2.
0 – 500 V
8451
E1
4 O
REGULATING
AUTOTRANSFORMER

0 – 500 V
E2
O 4
0-415 V
P1
3 phase
Q1
P2
5 O
8349
8329
8446
8446
O 5
8821
8821
6 O
0-415 V
Q2
Fig. 14 Sender and Receiver voltages equal, but out of phase
19
O 6
3 phase
Table 2
Tap Switch
E1
P1
Q1
E2
P2
Q2
Position in
degree
V
W
var
V
W
var
Phase angle
in degree
0
+ 15
-15
Does this experiment proves the statement that real power flows from the leading voltage
towards the lagging voltage side of a transmission line?
 Yes
 No
(Caution!! First DIRECTLY SWITCH OFF the main power supplies of both sending end and receiving
end and then set the supply autotransformers to zero voltage. Make changes in connection for
PART-III)
PART-III: Sender and Receiver voltages unequal, and out of phase
In the following steps we shall connect passive loads (resistive, inductive, and capacitive) at the
receiver end of the line. The object of the experiment is to show that a phase shift between
sender and receiver voltages occurs only when real power is being delivered to the load.
14. Using only one console, set up the experiment as shown in Fig. 15, setting E1 = 380 V and
using a star-connected Resistive Load of 1200  per phase and a 200- Transmission Line.
Take readings and record your results in Table 3
0 – 500 V
E1
8451

0 – 500 V
E2
4 O
0-415 V
P1
3-phase
5 O
P2
Q1
8446
8329
Q2
8446
8821
LOAD
8311
8321
6 O
8331
Fig. 15 Transmission line with different loadings
20
15.
Repeat procedure step 14 using an Inductive Load of 1200 /phase. Take
readings and record your results in Table 3.
16.
Repeat procedure step 14 using a Capacitive Load of 1200 /phase. Take
readings and record your results in Table 3.
Table 3
Step
14
15
16
Load
E1
P1
Q1
E2
P2
Q2
Phase shift
V
W
var
V
W
var
degree
RESISTIVE
INDUCTIVE
CAPACITIVE
Exercise
1. A three-phase transmission line has a reactance of 100  and at different times
throughout the day it is found that the sender and receiver voltages have magnitude and
phase angles as given in Table 4. In each case calculate the real and reactive power of the
sender and receiver and investigate the direction of the power flow. The voltages refer to
line-to-line voltages.
Table 4
SENDER
ES
ER
kV
kV
100
120
100
120
120
100
100
120
100
100
Phase angle
RECEIVER
P
Q
P
Q
MW
Mvar
MW
Mvar
60 ES Leads ER
60 ES Leads ER
60 ES Leads ER
30 Es Lags ER
0°
2. In Question 1 assume that ES = ER = 100 kV at all times but that the phase angle between them
changes in steps of 30° according to the Table 5. Calculate the value of the real power in each
case as well as its direction of flow, knowing that ER lags ES in each case. Plot a graph of real
power versus phase angle. Investigate the limit to the maximum power which such a line can
deliver under static voltage conditions.
21
Table 5

SENDER, P
RECEIVER, P
degree
MW
MW
0
30
60
90
120
150
180
3. Discuss briefly what you have learnt from this experiment.
Marking Scheme
Lab
(10%)
Assessment
Components
Details
Hands-On & Efforts
(2%)
The hands-on capability of the students and their efforts
during the lab sessions will be assessed.
On the Spot Evaluation
(3%)
The students will be evaluated on the spot based on the
theory concerned with the lab experiments and the
observations.
Lab Report
Each student will have to submit his/her lab discussion sheet
and recorded experimental data on the same day of
performing the lab experiments.
(5%)
22